The spinal column is a flexible chain of closely linked vertebral bodies. In a normal human spine there are seven cervical, twelve thoracic and five lumbar vertebral bodies. Below the lumbar vertebrae are the sacrum and coccyx. Each individual vertebra has an outer shell of hard, dense bone. Inside the vertebra is a honeycomb of cancellous bone containing red bone marrow. All of the red blood cells, and many of the white blood cells, are generated inside such cancellous bone, where the blood cells mature before being released into blood circulation.
The spinal disc serves as a cushion between the vertebral bodies so as to permit controlled motion. A healthy disc consists of three components: a gelatinous inner core called the nucleus pulposus; a series of overlapping and laminated plies of tough fibrous rings called the annulus fibrosus (or “annulus”); and two (i.e., superior and inferior) thin cartilage layers, connecting the disc to the thin cortical bone of the adjacent vertebral bodies, called the end plates.
The spinal disc may be displaced or damaged due to trauma or disease, such as a herniation or degenerative disc disease. A herniated disc may bulge out and compress itself onto a nerve, resulting in lower leg pain, loss of muscle control or paralysis. To treat a herniated disc, the offending nucleus portion is generally removed surgically.
Disc degeneration gradually reduces disc height, forcing the annulus to buckle, tear or separate radially or circumferentially, and causing persistent and disabling back pain. Degenerative disc disease is generally treated by surgically removing the nucleus and fusing the adjacent vertebral bodies so as to stabilize the joint. In either case, whether removing some or all of the nucleus, these procedures ultimately place greater stress on adjacent discs to compensate for the lack of motion, which may in turn cause premature degeneration of those adjacent discs.
It has been recognized that it may be possible to replace the excised nucleus with a prosthetic implant, whereby to restore the spinal disc to its original configuration and function. Unfortunately, such implants, sometimes referred to as a prosthetic nucleus, tend to suffer from one or more deficiencies.
One deficiency of current prosthetic nuclei is that the annulus is further weakened by either large or multiple cut-outs which are required in order to insert the prosthetic nucleus into the interior of the spinal disc. Additionally, any flaps or cut-outs of the annulus are not easily repaired.
Modern trends in surgery include the restoration of bodily function and form (i.e., the repair) of anatomical structures through the use of minimally invasive surgical techniques. The ability to surgically repair damaged tissues or joints, creating as few and as small incisions as possible, generally produces less trauma, less pain and better clinical outcomes for the patient.
Accordingly, there is a need for improved systems and techniques for repairing damage to the annulus, particularly when a small incision is made in the annulus for the insertion of a prosthetic disc.